Taking Back The Crown
by AlabasterTorrington
Summary: When a magical artifact gives Nico di Angelo back his memories of his past lives, as well as their powers, how will he cope with them? As well as dealing with the betrayal from the camps? With only Hazel, Frank, and the voices in his head, he must travel to find his past and attempt to stop a war between gods. Rated T for language
1. New Memories

**This is my new story, it will be a crossover between Attack on Titan, Undertale, and Percy Jackson. Read the bottom author's note if you want to know what happened to my other story.**

Nico was playing with his new pet, a cute little hellhound pup. He had found it in the underworld, all alone, and brought it back to camp. It had no teeth, and it was starving as it had no mother to give it milk, so Nico took it in and fed it. He found out that the hellhound was a she, and as a joke, named her Jr. O'leary. The camp in general did not approve of it, but as there already was a tame hellhound, Chiron allowed Jr to stay, on the condition that Nico had to make sure it was trained.

However, less than a month after Nico got her, he had to leave her for a while on a quest, with Thalia and Percy. They were traveling by the Lethe, to get to an artifact, a stone that apparently was the counter to any liquid, as long as the stone was in contact with both the liquid and the person/people at the same time. This artifact was currently in possession of the Keres, who did not wish to let it go, as this would lessen their domain, as less poison deaths would occur.

When they found the artifact, they realized that the Keres actually were at a battlefield currently, and they could just grab the stone and run, which they did. The Keres were back nigh instantly, however, and in the rapid struggle Nico was pushed into the River Lethe. As soon as Nico was submerged, a swarm of memories entered his mind, of dragon skulls firing lasers at a child, of chopping at giant, naked humans, of being tied up in vines and having the soul sucked out of him, of soaring through the air, dodging bullets and killing other humans. Many other memories flew through his mind at the speed of thought, with many dead standing out.

Nico climbed out of the river, holding the stone to his gash to deal with the Keres poison, and summoned a trio of bones, sending them flying at one of the Keres, causing it to fall to the ground, shrieking with pain. Nico went to draw his sword, then cursed as he realized it was at the bottom of the Lethe, along with his shirt. It didn't matter, as Percy and Thalia had already wrapped up the fight, and they headed back to camp.

When they had presented the stone to Chiron, and been informed that a feast was being planned to celebrate their success, they headed back to the cabins to rest, and prepare for the capture the flag game with the Hunters. When Nico lay down, he started to ponder on the new memories he had gotten. He had lost his blade, but he had gained something far more valuable to him, memories of his mother and Bianca. **(A.N. in this story, demigods can look back at their memories like they were movies)** He smiled as he looked back on himself playing tag with Bianca, screaming with laughter as their mother looked over at them, smiling.

Then he got to the darker memories, like watching a skeleton's head get chopped off, his body dissolving into dust, shortly followed by his head. He watched as a child walked up in front of him, with a dusty knife in their hand. They lunged forward, again and again, as he grew tired, until one of the odd attacks that he kept summoning hit the child straight in the face, and they died. However, there was an odd jump of some sort, and he suddenly was back at full strength, and the child was smirking at them. He threw the child into the wall without touching them, somehow, and bones sprang from the wall, impaling them through the chest. They got up, however, and a dragon skull popped into existence, firing a laser beam through the child's heart. They did not get back up. The jump happened again, and the memory shifted.

A massive humanoid, naked, appeared in front of him, on a grassy plain. He fired hooks from the odd holsters at his sides, pulled twin blades out of the holsters, and swung around the being, which I somehow knew as a titan. I spun, the blades spinning as i slashed through the back of the titans neck, dropping it to the ground, dead. Other scenes appeared of more titans eating people who I knew, getting killed, and even some humans transforming into titans.

Two presences appeared in my mind, and spoke. One simply sounded like a human, the other chattering like a skeleton. The human spoke first " _I'm Levi,"_ then the skeleton " _Heya kid. I'm Sans."_

 **So tell me how much you like it! This is going to wind up as another betrayal story, as I feel like I seriously screwed up my first one. That story will be up for adoption, PM me if you wish to take it.**


	2. Don't Worry, You Aren't Insane

**So for those who didn't understand why the Lethe gave Nico's memories back, that's the artifact's power. If it is in contact with both a person and a liquid, and the person is touching the liquid, then the liquid will have the opposite effect on the person. So the Lethe water was reversed, and gave Nico's memories back. Characters will be OOC. Sorry for not saying this earlier, but this takes place after HOO, with some changes, and will use plenty of things from the AOT manga, though there will also be contradiction. Undertale AU's may make some appearances, as will some theories.**

As soon as Nico heard the voices, he passed out. As he lay there still, his mind was brought to a rather spartan room. In two chairs, sat two very different people. Nico sat down in a third chair, leaned forward, and asked the obvious question.

"Why the fuck are you in my head?"

The one on the left, which looked like a skeleton, yet anatomically incorrect, and Nico couldn't feel him with his powers replied first, and with a laugh,

"That's what I said, too. We are your past lives. We can look through your memories, you have access to ours and our powers, and if you are unconscious, or give us permission, we can control your body. This is one of the biggest reasons that children of Hades go insane, they are the only ones who can hear us. Thankfully, you were given the memories before you grew too old to accept them."

Nico looked warily at him, "So you can control me? I don't really like that idea."

"No worries," the skeleton shrugged, "I'm pretty done with life, anyways. By the way, to reintroduce ourselves, I'm Sans, and this here is Levi."

Levi looked at him with black eyes, so like my own, filled with repressed grief for the dead, and jaded from seeing so many of said deaths.

"Hey kid, nice job with freeing us, but how did you do it?" he asked.

"First off, a magic artifact, and an accident. Second, who are you to call me kid? You're as tall as I am!" Nico replied heatedly.

"That may be true, but I am older than you, as i am 34. And no, Lotus Hotel does not count." Levi snarked back.

That stopped Nico in his tracks. "You can read my mind?!"

Levi sighed, "This is your mind. We live here. Of course we can read your mind."

"Alright, alright, cool down everyone," Sans said, "Same side, k? So now, Levi, should i go first or should you?"

"I'll go first, as it should seem more familiar."

"Cool. So, kid, Levi is gonna give you his memories and abilities, all right?"

Nico nodded hesitantly. "Will this change my personality at all?"

"Possibly, but not directly, just from your reaction to this," Sans replied, gesturing at himself and Levi. "Our personalities won't become a part of yours."

Nico nodded again, more confidently this time, and all of a sudden, memories flowed through him. He managed to remain on his chair, and recovered rather quickly.

"Right, so now it's my turn. In this area, you cannot use our powers or abilities, and so you will feel stronger only when you wake up." Sans rubbed his hands together.

Again with no warning, the memories flooded his head, this time far more, several times as many.

"And now, you will awaken. We can still talk to you, and you may gain some of our features. We'll find out which later." Levi said tiredly. "I'll be sleeping for a while though, so you won't hear me talk at all for about an hour."

Nico bolted straight upright, smacking his face into the not so soft face of Percy Jackson. The ever so great Hero of Olympus, fell straight on his butt, groaning in pain. This caused laughter all around them, as Nico looked around, seeing the entirety of the Seven, as well as Reyna, seated around his bed, which he then realized was in the infirmary. Clearly, someone had found him.

" _Clearly,"_ Sans remarked.

" _You shut up now, k?"_ He thought.

" _Ok. Have fun explaining to your friends why you passed out,"_ He snickered.

Nico gave him the mental equivalent of the middle finger.

Percy sat back up, with a sigh at his friends, before looking at Nico with concern, "You ok, Death Breath? We heard a crash, and then we found you lying on the ground, knocked out."

"I'm fine, just some memories returning. Guess that this artifact really is dangerous. I remember my childhood now," Nico said with a smile. He remarked to Sans, " _I thought it would be best to not mention you two."_

" _Probably,"_ he agreed.

"That's great!" Hazel exclaimed, hugging her brother. Frank smiled at him from behind Hazel's head, showing his appreciation that Nico was alright. Nico smiled, hugging Haze back, before Percy tried to clear his throat, failing badly, and then started coughing. Annabeth laughed at him, before hitting him in the back loudly, stopping him.

"So Nico, the Hunters are back in Camp, and we are having one last CTF game before heading to Olympus for the Giant War gifts." Percy rolled his eyes. The gods had declared that the heroes would have to wait until after some construction had happened, and the throne room was fixed from the battle damage. Aeolus, controlled by Gaea, had attacked Olympus, but the combined force of Nemesis and Hecate had successfully defended Olympus, though not without damage to it.

"That definitely didn't take forever," Nico said sarcastically. "The gods don't want to present us our gifts in a destroyed room, Nico," Hazel admonished. "Be at least somewhat respectful."

"Sorry, sorry," Nico held up his hands in surrender. "I'll try."

Hazel smirked at him, knowing that she had won.

"So are we gonna play or not?" Frank broke in.

They laughed and jogged towards the forest, chattering about random things. When they arrived, Nico was told that he was on defense.

Defense.

One of the more boring jobs normally, but it was a necessary position, and you got plenty of action against the Hunt. The campers were admittedly awful, particularly the Olympian cabins, with the exception of Ares, Hermes, and Hephaestus. Apollo was decent, but their skillset was more based off of being able to trade out wounds extremely well due to their healing. As such, the Hunters kind of just ran right past them.

Nico was grouped up with the Hecate and Hephaestus campers, who decided to create a magical field. They used their knowledge of magic and metalworking to create a trench and wall all around the flag, followed by a magic barrier that prevented their being any silver in the area.

This meant that the Hunt would be almost completely unable to enter the area. Nico the summoned a good dozen skeletons to stand guard by the walls, as they couldn't really be hurt by arrows. Nico had also figured out that his geokinesis could be used on the Hunt's silver itself, meaning he could just fling everybody around.

As the horn blew for the start, Nico, Levi and Sans all said the same thing.

" **Let the battle begin."**

 **So I hope you enjoyed what you read. Frisk and Chara will make appearances, and they will both be female. Undertale is both real and a game, so there will be people who recognize the monsters, and AOT is the same, with the location being on a remote island. Titans are currently extinct, but will make a reappearance.**

 **Please review with any ideas on where the story should be going.**


	3. Spooky Scary Skeletons

**Thank you for the support on this, and in particular to dog1056, who left an amazing review that gave me some ideas, as well as inspiring me to write. In answer to some of your questions, the non-canon backstory will in fact be explained through Nico's dreams. Undertale's cast is almost completely dead, including Papyrus, though he may make an appearance as a ghost. Levi will not affect Nico's sword style, and finally the betrayal reason will be explained in this chapter. Others cannot be answered due to spoiler reasons.**

As the horn blared out for the start of the game, shouts immediately broke out as campers charged, yelling war cries that did absolutely nothing as arrows started hurtling through the trees in response, crashing into campers without mercy. The campers wilted under the heavy fire, with only a few making it through the hail, and just a few more than that making it back to cover. Just like that, a good half the campers had been knocked out by the blunt arrows.

The attacking force went on in shambles, attempting to cover themselves with their shields, as they knew that stealth would be of little use against the Hunt. The defensive force retreated under the magical field, hoping that it would hold until they could create a counterattack. Of course, the Hecate campers saw fit to tell them then that it only would work as long as there was someone conscious under it. This was a huge problem, as the Hunt could simply make stone arrows and shoot them from outside, then just walk in and grab the flag.

With some help from Levi and Sans, Nico hatched a plan. Chiron had forbid shadow travel, as it was considered "overpowered" since Nico would be literally unbeatable. So instead, Nico summoned a skeletal deer, then had one of the two remaining Hecate campers cover it in Mist to give it the appearance of a normal deer. The deer would be able to, in theory, sneak in and grab the flag while they focused entirely on defense. The problem was that everyone else had been taken out and the hunters were right there. Fortunately, the deer had already been sent off, so they didn't see it. Nico figured they had at most two minutes before they figured out how to deal with the barrier, and then they would be in trouble. Turned out, while the other hunters went to gather stones for arrows, Thalia figured it would be a great idea to fry everyone she could. This, of course, resulted in everyone but Nico and the Hecate campers to be shocked unconscious.

With this amazing development, a barrage of arrows hit them from behind. The last campers had been knocked out, and Nico was the last man standing, literally. The Hunt circled around and came together as one group. Percy had only managed to solo about a third of them, which was pretty damn impressive, but nowhere near enough. Either that, or the others were defending, which was a scary thought, as i meant that they had lost for sure. Thankfully, the Hunt knew that they had to play aggressive, as they lacked the numbers to whittle down the camp's numbers. Therefore, it was unlikely that they had many on defense, if any at all.

The hunters were conferring, knowing they had all the time in the world, or at least most of it. One of the older ones smirked, said something, and caused the whole Hunt to giggle evilly. Nico tensed, knowing _something_ was up, just not what it was. He would soon find out, though, of that he was certain.

The biggest hunter stepped forward, and started talking. The words streamed from her mouth like poison, hateful and full of malice, only designed to hurt. The words she was saying hurtled around in his head, bouncy balls constantly smacking into his emotions, bringing out all the hate he held for the Hunt. " _Bianca's little precious," "Bianca's killer," "Bianca's brat,"_ and other similarly crushing statements. Nico shook himself, attempting to remove the sting of the words, discovering that he had tears running down his cheeks, and the hunters laughing at him, taunting him more and more. All of them had joined in, even Thalia, and it stirred the flames of his rage. The Hunt had taken his sister, then gotten her killed. Then they hadn't even acknowledged her sacrifice, heaping all the praise on everyone else. And now, they had the sheer audacity to mock him for it?! As he fumed, Sans spoke in a dark voice,

" **Let me."**

Nico stepped back and allowed Sans to take control, hearing the absolute **hate** in his voice at these people, who would torment a young boy about his dead sister, whose death they were responsible for. His appearance started to change, with his left eye beginning to glow an eerie blue, and his right eye becoming pitch black, no pupil visible. His skin, pale to begin with, went full out bone white, and his smile stretched to larger than should've been possible, with all of his teeth showing.

The Hunt noticed the change in him, and some of them began to feel somewhat nervous, like they were doing something that would get them killed, but they shrugged it off and continued taunting him. Thalia in particular became very nervous about what was happening, and started sweating. Then. Then he started speaking, and all of them shut up. His voice was terrifying, the voice of a god, the voice of the person who decided your fate. _The voice of a judge_.

" **So, we have some little girls who decided to try to mock me, hmmm? Well guess what. Today, I'm going to show you what happens to a little dog who barks too much at a bigger dog."** Sans' voice echoed around the forest, dark and terrifying.

The Hunt started laughing. Doesn't matter how scary your voice is, in the end it's one against a good twenty. Then they all got lifted into the air at once, and they stopped laughing. Then got thrown into trees. Then odd, draconic skulls appeared around each of them. At the end, they were looking at him with fear, which doubled when the skulls opened their maws and light began gathering in each of them.

The big hunter, Nico remembered her name to be Phoebe, tried to pull a bow, but then the skull unleashed its blast, and within the span of half a second, blew her bow to pieces. The skull already had another blast ready by the time she registered what happened. Bones flew up from the ground, and encircled her, ready to stab her if she tried anything else. However, something caught their attention, which was the deer sprinting back with their flag firmly in its teeth. The deer walked over to Nico, dipped its head, and proffered the flag to him. He took it, and smirking, placed it with his own flag, whereupon it turned to pitch black with the helm of darkness on it **(In this CTF, you must put the opponent's flag with yours, to make it a more difficult game)**. He walked back to them, sighing, then said to the deer,

"Isn't is sad the way that assholes never win? Oh true, I guess I'm wrong, they do win quite a lot, but only if they have powerful friends. Such a shame that i don't give a shit about said friends."

Nico laughed crazily, as Sans retreated back into his mind, due to the massive power rush he was experiencing right then.

However, he turned around at the sound of a cough, and saw the entire council, with Apollo and Hermes giving him discreet smiles and thumbs up, Hades looking rather proud, Ares and Aphrodite struggling to keep from laughing at the situation the Hunt was in, and Artemis along with everyone looking absolutely furious.

Nico looked at them all, smirked, bowed, and said smugly, "There's one for Camp Half-Blood."

 **That's the end of this chapter. Please do review, as it is quite nice to have input from other people about which way the story could go. Again, thank you to dog1056 for the amazing review, and have a good time!**

 **P.S. I am a fan of Good!Chara and Evil!Frisk, so, fair warning.**


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